Issue 30

V. Crupi et alii, Frattura ed Integrità Strutturale, 30 (2014) 569-577; DOI: 10.3221/IGF-ESIS.30.68

Crupi [16] developed a theoretical model able to describe the temperature evolution during the phases 1 and 2 of the fatigue life:

  

  

     N

as e T T 1

(1)

d

where  is a constant; if N is  then  T d . The value of 4  , applied successfully to conventional steel under HCF loading in [16], was considered also in the investigated VHCF tests. The  T d - N data were interpolated by means of an exponential function according to eq. (1) and the convergence was achieved, as demonstrated in fig. 3 for 115CrV3 and for 60SPb20+Bi. As can be seen, for both materials there is a strong correlation between the experimental data and the theoretical ones. is 0,63  T as and if N is 4  then  T d is 0,98  T as

Figure 3 : Experimental and theoretical ΔT d - N curves. Fig. 4 shows the values of asymptotic temperature increment during fatigue test ΔT as (phase 2) as a function of the square of stress range applied Δσ 2 for the two investigated steels: 115CrV3 and 60SPb20+Bi. The behaviour of the 60SPb20+Bi is a confirmation of the linear trend in VHCF tests, the same already observed in the HCF tests [6, 14, 15, 16]. However, it is interesting to note that the 115CrV3 steel has a different trend, even if more tests should be necessary.

vs Δσ 2 .

Figure 4 : ΔT as

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